Few animals may seem to be as far apart on the spectrum when it comes to similarities as a whale and a bird. Birds fly through the sky with the help of their feather covered wings and flippers make it possible for whales to maneuver through the ocean. But the wings of a bird and flippers on whales are much more similar than you may think. In fact, both tetrapod limbs are a homologous trait that they inherited from their common tetrapod ancestor. This ancestor, the first tetrapod, is believed by scientists to have roamed the Earth 350 million years ago and had limbs with one humerus attached to the radius and ulna.
Unlike the obvious lack of similarities between whales and birds there are some animals that look strikingly similar but are very different such as the Northern Flying Squirrel and the Sugar Glider. These two animals live in separate parts of the world. The Northern Flying Squirrel lives in North America and Sugar Gliders are found in Australia but they share analogous structures. They are both nocturnal and have big eyes to assist them in seeing at night and a thin piece of skin that stretches between their arms and legs to help them glide when leaping from high places. Though these very distant relatives look so much alike the are quite different. The Sugar Glider is a marsupial mammal and give birth to their young very early and provide most of their nourishment in their pouch as their baby develops. Northern Flying Squirrels are placental mammals that spend a much greater deal of time developing in their mother's body being nourished by their mother's placenta. If we go far back enough, we will see that these two animal so in fact share a rat like common ancestor which is the Mammalia.
I would have liked expansion on how the structures of the eagle wing and the whale fins actually help in their given environments? You mention the skeletal similarities but the skeletal differences would have provided a clearer picture of the divergent evolution in this example.
ReplyDeleteDo we need to go all the way back to the first tetrapods to find a common ancestor? Bird and mammals both arose from archaic reptiles, who also share that ancestral limb structure and passed it on to these two descendents. That is all we need to know to confirm the ancestry on these homologous traits.
The flying squirrel and the sugar glider are one of my favorite analogous pairings! Good descriptions on the traits. However, remember that part of the information we need is that these traits are not the result of common descent. Yes, they have a common rodent ancestor, but did that ancestor possess this trait? Did these traits evolve independently from each other?
Great images.